WorldWide Drilling Resource

38 JANUARY 2019 WorldWide Drilling Resource ® Constructing a Water Well Adapted from Information by the University of California The process of designing and constructing a water well begins when arrangements are made with a licensed drilling pro- fessional or consultant who will design the well and oversee the work of the drilling professional. After a suitable location is established, the drilling rig is set up. In California, the most common drilling techniques are rotary, reverse rotary, air rotary, and cable tool. For shallow wells which are not supply wells, auger drilling is often used. In unconsolidated and semiconsolidated materials, rotary, reverse rotary, and cable tool methods are commonly employed. Cable tool drilling generally is less labor-intensive, but it takes more time than reverse rotary or rotary drilling. Reverse rotary and rotary drilling requires large amounts of circulation water and the construction of a mud pit, which must be considered if the well is to be drilled in a remote location with no access to water. Hardrock wells are gen- erally drilled with air rotary drilling equipment. Properly implemented, all of these drilling methods will produce equally efficient and productive wells where groundwater is available. Sometimes a small-diameter pilot hole will be drilled before the wellbore. From informa- tion obtained from the pilot hole, aquifer formations and groundwater quality at various depths can be determined, then the final well design can be optimized for the specific hydro- geological conditions at the site. During drilling, a detailed log of the drill cuttings from the advancing borehole must be kept. In addition, after drilling has been completed, but before the well is installed, it is often desirable to obtain more detailed data on the subsurface geology. This can be done by taking geophysical measurements in the borehole. Specialized equipment is used to measure the electrical resistance, as well as the self-potential or spontaneous potential of the geological material along the open borehole wall. The two most important factors which influence these specialized logs are the texture of the formation and the salinity of the groundwater. Sand has a higher resistance than clay, while high salinity reduces the electrical resistance of the geological formation. Careful, professional interpretations of the re- sistance, spontaneous potential logs, and descriptions of drill cuttings provide valuable information about water salinity, location, and thickness of the aquifer layers. The information obtained is extremely useful when finalizing the well design, which includes a determination of the depth of the well screens, as well as the size of the screen openings and gravel pack material. Once the wellbore is drilled, well casing and well screens are installed, then the annulus around the casing is filled with a gravel filter pack and the appropriate cement and bentonite seal. This prevents water from leaking between uncontaminated and contaminated aquifers, as well as from the surface into the well. Next, the drilling professional develops the well, imple- ments an aquifer test, completes the sanitary seal of the wellhead, and installs a pump and power source. Proper design, construction, development, and completion of the well will result in a long life for the well and efficient well operation. WTR It takes 75,000 crocus flowers to produce one pound of saffron, which is why it is the most expensive spice in the world. All of earth’s continents are wider at the north than the south. The spots of light you see when you rub your eyes are called phosphenes. The brain uses more than 25% of the oxygen used by the human body. Any free-moving liquid will form itself into a sphere in outer space because of its surface tension.